Geiger-muller tube mounting



March 20, 19 51 M. J. TEST ET AL 2,546,048

GEIGER-MULLER TUBE MOUNTING 2 Sheets-Sheet 1 Filed Jan. 12, 194:8

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175551 EST- MEYEE SI/ELL'EY M. J. TEST ET AL.

GEIGER-MULLER TUBE MOUNTING March 20, .1951

Filed Jan. 12, 1948 give rise to serious difliculties.

Patented Mar. 20, 1951 UNITED STATES PATENT on 2,546,048 ICE GEIGER-MiJ'LLER TUBE MOUNTING Original application October 1, 1941, Serial No. 413,241. Divided and this application January 12, 1948, Serial No. 1,708

13 Claims.

This invention relates to a light compact portabl apparatus for indicating gamma ray intensity. It is an object of the invention to supply such an apparatus which will at all times indicate the intensity of gamma rays on a dial, which will be completely portable, and simple in operation.

It is a further object of the invention to provide an apparatus which will sound a signal or light a signal lamp whenever the intensity in the vicinity exceeds a safe value.

It is a further object of the invention to provide such an apparatus with a definite operating characteristic so that it will sound an alarm for the same value of gamma ray intensity at all times.

. It is a further object of the invention to provide an apparatus which will have several ranges of operation.

It is a further object of the invention to provide a mounting for a Geiger-Muller counter tube so as to provide for easy interchanging of the said tube.

It is a further object of the invention to provide a simplified form of mechanical construction for an apparatus using a Geiger-Muller counter tube.

It is a further object of the invention to provide" an apparatus with a suitable accurate integrating circuit so that the number of pulses indicated may be recorded upon a dial and read conveniently.

It is a further object of the invention to provide an apparatus and system upon which an alarm will be sounded at a. distant point whenever the gamma ray intensity in the vicinity exceeds a safe value.

The harmful effects of gamma rays produced by radium and similar radioactive substances, and of X-rays having properties analogous to gamma rays, have long been recognized. Workers handling such preparations or working in the vicinity of X-ray machines are often subjected to dangerous conditions. This is all the more serious in view of the fact that gamma rays and X-rays produce no sensation and may give rise to considerablebodily damage before any sensation whatever is felt. It is further well recog- 2 noyance connected with such measurements dis-. courages their use, particularly under the pres sure of work.

The apparatus described in the present invention is intended to obviate these difficulties. This apparatus is so constructed that it operates continuously. It need only be connected to the standard power supply and left in the operating condition. Thus, whenever the gamma ray intensity in the vicinity exceeds a safe value, a definite alarm, both visual and audible will be given and users in the vicinity will be warned of the dangerous conditions which exist. This alarm will continue to operate until the dangerous conditions have been rectified. The apparatus will operate no matter what the direction of the incident rays and no matter whether the dim-.-

nized that a number of rather small doses, re-

ceived constantly or' continuously by a worker working in the vicinity of unshielded radium can Recent investigations' have in fact shown that serious genetic changes may be caused by very small repeated doses, much smaller than those considered in the prior art to be of any serious nature. These facts make it important to have an apparatus which will indicate dangerous conditions.

The prior art apparatus, while capable of detecting such conditions, required the attendance of an observer and the deliberate making of measurements from time to time to determine whether dangerous conditions existed. The anculty is caused by one concentrated source or by a number of small sources producing an additive effect. w

Reference is had to the accompanying drawings in which:

Figure 1 represents a general perspective external view of the apparatus.

Figure 2 shows a side view of a portion of the apparatus when removed from its outer protec-.- tive case.

Figure 3 shows a front view of the case, with the front panel removed.

Figure 4 shows a mounting for the Geiger- Miiller counter tube.

Figure 5 shows the wiring diagram for the apparatus.

The entire apparatus is contained within a case I, which may be of wood, plastic, or other suitable substance, but which is preferably made of metal. Steel has been found a suitable ma terial. The front of the case I has a sloping face upon which are mounted the control and indi cating elements. In the center is a meter 5 upon which the intensity is indicated at all times. To the left of this meter is a pilot lamp 1, to indi-; cate whether or not the instrument is operating. At the right part of the panel is a warning light 8 which becomes illuminated when the intensity has exceeded a safe value. In the lower part of the panel is a switch 6, which controls the current input and a switch 9 which controls the alarm circuit. Screws I0, hold the the front panel to theremainder of the case I and are removed whenever it is desired to remove the operating parts thereof. A handle 2 is affixed rigidly to the top of the case. The front part. of the panel is fastened by means of screws ll to a spacer block l2, which is in turn fastened to a frame or chassis I3. In the rear part of the chassis 13 is a removable plug [4 which is con nected to the power cord 3, which in turn terminates in a standard attachment plug 4. The

front part of panel 30 is thus fastened to the.

chassis I13 in .suchfashion that the entire :assemblage may be removed as a unit without detaching any of the connections between the units mounted on panel 30 and chassis L3. The case I has in its front part two longitudinally extending flanges [9, in which arelprovided tapped holes 20. These flanges extend for only lthe sloping portion of the case I. Screws H], are threaded into holes 2!] and thus serve to-hold the entire removable assemblage in place. In the upper part of the case:& are provided ventilating openings 3], also circular openings 16, I! and I8. Opening [6 is so placed .as to be in alignment with the opening in the rear part of the chassis 13 for receiving the power supply cord. Similarly opening [8 aligns with a receptacle in the chassis for receiving the cord to an external circuit. Opening ll is coincident with the position of a control element on the rear part of the chassis I3. Thus, after the cordsfhave been removed, there are no connections hindering the removal of the entire working assemblage. During the operation of the ap'paratuaheat is produced by the various elements and it is found desirable to dissipate this hea't'eifectively. This is particularly desirable in view of the fact that the resistances used in "difierent parts of the support have appreciable temperature coefficients. Thus, if sufiicient ventilation is not provided, the resistances will change their'values depending upon the external temperature, the .radiating properties of the unit, and thelength of time the apparatus has been operating. Toobviate these eifects, the bottom of the case i is provided with a series of openings. 'To'prevent solid particles from entering these openings and causing disturbance in the electrical system, a piece of wire netting or screening 32 is fastened to the bottom of the inside of case I. Chassis I3 is provided with a series of ventilating openings in the upper surface 33. Thus, in operating, a current of air will be'rirawn from the lower part of the apparatus due to convection, will circulate through the chassis l3, and escape through ventilating openings 3 l. In cases in which considerable dust exists, it may be necessary to mount a plate almost entirely covering netting 32, but raised an appreciable distance therefrom. By this, the air'willbe forced to follow a tortuous passage and relatively little dust will be carried thereby. In cases in which considerable radioactive dust exists in the vicinity, this latter precaution is necessary and it may in fact be necessary to seal the entire apparatus tightly. In this case, it will be allowed to attain thermal equilibrium bybeing left on for a suitably long time after which reliable measuraments may be made.

"The mounting of the Geiger-Muller tube used in'the apparatus is one that has caused some difficulty in the prior art. Such tubes were usually'held' by clamping means and were provided with soldered connections. It thus required virtually the services of an instrument maker *to replace 'a tube. It has been found that su'ch a tube maybe conveniently and eifectivel'y mounted in a standard vacuum tube base, and thus conveniently removed and replaced by relatively unskilled personnel. An effective means of doing this is shown in Figure 4. 'Here avac'uum tube base 2!, preferably of a low loss plastic'an-d of a four 'pronged variety, is turned toithe shape shown and bored to receive a tube 22. The tube 22 maybe of metal, in which case his fastenedto one of the prongs 34, and ground- :ed within'the apparatus to avoidhcapacity disturbances. The Geiger-Muller counter shown schematically as 24 is placedwith its terminals .projecting downwardly and these terminals are connected respectively to prongs 27 and 2B. A

.metallic cover 123 is .provided, upon which may beimarked theserial number of the tube and its important characteristics. The tube 24 is preferably covered with some highly insulating wax such as Superla Wax manufactured by the Standard Oil Company of Indiana. This wax will prevent leakage due to moisture adhering to the surface of the glass. The enclosure formed bytube 22, base 2!, and top 23, serve another important function. 'Ihey prevent the admiss'ionfofdus't :tothe Geiger-.Miiller tube. This is very important since in m'any cases "the apparatus will ibeused'in plants'in which the dust will co'ntain appreciable quantities of radioactive 'materials. This dust will adhere to the usual Geiger-Muller tube and cause it to develop a: high background which will make measurement'imore difllcult. The facility with which the Geiger=MiillertubeLmay be changed allows spare tubes to be kept and *allows the instrument to be 'checkedrea'dily by substituting a new "tube and "observing the behavior of 'the instrument. This oproc'edure :took .a prohibitively long time with "prior. art structures.

Where it is desired :to make the apparatus in- S'flIlSltiVe'ltO betaraysfas. maybe necessary when measurements are made on strong radioactive sources, xthe outer iprotectivemovering '22, and the'cover23*may'beimacle :of lead-1 centimeter 'or'more'ofithickness. 'In such cases, a lead disk could be placed at the bottom of the cavity in insulator Ziywith openings for the lead wires. Such ashiel'd will effectively-exclude any beta rays which might not be stopped by the outer case i, orth'eair between the source and the Geiger Miilier tube. A removable'shield, fitting closely over the assemblage shown in Figure 4 and made of'l'ea'd of approximately 1 centimeter thickness may also be utilized. It is'understood that leader other shielding or filtering materialrnay'be placed within the interior of case I, andffastened to'the walls thereof so as to-serve the same function as'the shield surrounding element 22. A similar constructionmay be utilized tomake the apparatus directional i. e. to make the response chiefly to rays from a given source. In such'ca'ses, theshielding material coul-dbe excluded from one side of the case or one side of the tube'22, making the apparatus especially sensitive to rays from that direction.

Referring 'now'to Figure 5, 29 represents a power transformer of a conventional type. A receptacle {i5 is providedthrough which current'enters through a fuse 36 and an on-off switch 6. This is directly across the primary 38 of transformer 29, and also has across it a small neon lamp 3?, to indicate whether the power is on or off. Although an ordinary incandescent lamp may be utilized, a neon lamp is desirable because of the limited current drawn and'the limited heat produced thereby. Filament windings 4i! and 4| are provided. These are connected in conventional fashion to the vacuum tubes as shown. A high voltage winding 42 is connected to a rectifier 43. This may be-a usual full Wave rectifier type, but is not utilized inthe conventional-way. One half of this rectifier provides the voltage for the plates of the vacuum tube while the other side provides the voltage for the Geiger-Muller counter. The

across the supply line.

rectifier 43 is preferably a type which operates directly from the high voltage supply current, and has its filament terminals 44 connected Cathode 45 is connected through resistor 46 to the central wire 41 of Geiger-Muller counter 24. Theout'er cylinder 46 of the Geiger-Muller counter is connected through resistor 49 to ground. A blocking condenser 56 is connected between the outer cylinder 48 of the Geiger- Miiller tube and the grid 5! of vacuum tube 52. A resistor 53 is connected between the grid 5! and ground. The Geiger- Miiller counter is supplied with a constant high voltage through the regulator system shown. This consists of vaccum tube 54, and voltage regulator gas discharge tube 55, connected through resistors 56 and 51 as shown, to the terminal of the resistor 46. One terminal 53 of voltage regulator tube 55 is connected to ground while the other terminal is connected to cathode 59 and tube 54. A discharge of the Geiger-Muller counter 24 by the action of gamma rays, cosmic rays, or X-rays, produces a positive voltage pulse across tube 66. This pulse is amplified by tube 52, which acts as a resistance capacitance coupled amplifier. The tubes are operated at that portion of their characteristic, such that they are overloaded. Under these conditions, the output pulses will be of the same size regardless of the value of the input pulses. This also follows from the fact that the plate voltage has been stabilized by the voltage regulator 55. The amplified pulses are rectified by the diode portion 6| of tube 60, and the rectified pulses charge condenser 62. This further results in the charging of condenser 63 to a voltage whose magnitude is proportional to the frequency of repetition of pulses produced by the Geiger-Muller counter 24. The voltage across condenser 63 is fed directly across the step ladder attenuator 64, consisting of a number of resistances in series. The voltage from the switch 65 across attenuator 64 will be applied across one side of tube 66. One portion of tube 66 is connected to amilliammeter 5 as shown, and the output of this portion of tube 66 will thus be fed across the milliammeter 5 and will give a reading which is proportional to the voltage on the grid 68 of this section of the tube 66. Since this former voltage is proportional to the frequency of pulses produced by the tube 24, the reading on the milliammeter will therefore be proportional to the frequency of the pulses. It can be seen that the plate circuit of tube 52, including element 54, comprises a circuit operated by the radioactive sensitive member 24. A potentiometer 65, connected to the meter 61 as shown provides a zero setting for the meter. The circuit containing the potentiometer 69, together with its source of voltage at element 84, may be termed a bucking circuit. This bucking circuit, it will be seen, applies a voltage counter to that applied to the milliammeter 5, and therefore opposes the voltage applied to the milliammeter. The source of voltage for the bucking circuit is obtained from the voltage divider composed of resistors 84 and 85, which derive their voltage from rectifier tube 43 through voltage regulator tube 55. By proportioning the resistors 84 and 85 properly, the desired voltage opposite to that applied to the meter 5 may be obtained. The exact magnitude of this may be adjusted by means'of rheostat 69. Thus, it is seen, that a variable bucking voltage can be obtained, and can be used to set the meter to any desired value at any time.

By adjusting the position of switch 65, the range of the instrument may be changed. For instance, if the lower-most position shown is utilized, the instrument will be on its least sensitive range, since the voltage applied to grid 68 of vacuum tube 65 will only be a fraction of the total voltage across the condenser 63. In order to operate a relay, lamp, and buzzer so that the latter units will be actuated when the frequency of the pulses reaches a predetermined value, an auxiliary unstable circuit is utilized. This makes use of a gas discharge tube 10, which is connected to one side of vacuum tube 66 as shown through resistor H. A condenser 13 is placed across the elements of the discharge tube 76. The discharge tube 15, being supplied with voltage as shown, will oscillate periodically by virtue of the resistance and capacity connected thereto, and the frequency of the oscillations will be dependent upon the relative values of capacity and resistance. This oscillation is rectifled by one of the diode elements 14 of tube 66. The consequence of this is that the potential of the grid 55 of Vacuum tube 66 is raised to a high negative value, making the current through the relay coil of relay '56 very small. When the grid voltage applied to grid ii of tube 66 becomes more negative due to increase of voltage across condenser 63, the voltage drop across resistor-H decreases until it is insufficient to supply the gas discharge lamp ii], at which time the oscillation in this circuit ceases. The voltage across condenser '56 therefore becomes zero or a very low value. When this occurs, sufiicient curent flows through tube 65 to energize-the coil ofrelay 16. The relay will therefore close contacts 19 and 86, operating a low voltage lamp 8, a buzzer 82, and and external alarm connected across the alarm outlet 63. A switch 9 controls the buzzer and may be opened if desired. The lamp 8,

buzzer 82, and any external device connected across the alarm outlet constitutes singly or in combination, means actuated by the sensitive member 24 and oscillatory circuit containing elements l6 and 13 jointly.

Use of the gas discharge lamp and its local associated circuit therefore provides definite operation, which will take place when a certain definite counting rate has been reached. With prior art devices, the current through the relay coil of a relay such as 16 would be provided directly from the plate of a vacuum tube. The operation of the relay would be indeterminate since a relay will not always pull in with exactly the same current nor will it always open for the same value of current drop. The effect of the auxiliary circuit with the gas discharge lamp is to provide a sort of sharpening circuit, one which will function accurately. Whenever the applied voltage, dependent upon the frequency of pulses, reaches the predetermined value, there will be a sudden rush of current through the relay coil. As soon as the value drops below the figure desired, there will be a sudden resumption of the action of the discharge lamp and therefore 'the sudden dropping out of the relay contacts. The control 31 serves to adjust the exact value for which the relay will operate. This is done, as shown, by adjusting the potential of the-grid H of tube 66, relative to the cathode of the tube.

It is thus seen that an instrument has been provided which will receive the pulses from a Geiger-Muller counter and will indicate at all times on a meter the frequency of these pulses. The Geiger-Muller counter will be unaffected by .fluctuationsi'in line voltage as will ,theremainder of the circuit by virtue of the use of the voltage regulator system shown. The range of operation may, be changed, and the meter be made to read zero for a condition of noreceived rays. An

additional sharpening circuit has been providedso that the alarm elements will be operated very definitely to give an indication when the intensity has reached a predetermined value and will cease functioning when the intensity drops belowthat value.

It is obvious that anumber of changes and additionsmayqbe provided without departing from the spirit of the invention. Thus, another voltage regulator system'such as a number of gas discharge lamps in series may be provided across the voltage supply for the Geiger-Muller tube, in place of the specific regulator shown. The meter 61, may be a conventional recording type, made to record the values with passage of time and thus furnish a permanent record of the radioactivity. Such'records may be obtained in the absence of an observer and will indicate whether dangerous conditions have existed at any time in the absence of the observer or whether material has been removed. Such a recording device may also be placed near a storage depository for radioactive material and will indicate the time at which any material has been removed.

It is further obvious that the relay on closing may actuate circuits other than a simple alarm circuit. Thus, the unit when used in conjunction with Y-ray work can control the input X-ray tube current through the relay, ,and cause this current to become zero whenever the intensity exceeds a safe value. In this modification, the relay coil on being energized would open the contacts rather than close them. The relay may also operate a shielding member held in place by an electromagnetically operated latch. Thus, as soon as the value becomes too high for safety, the latch would beoperated and the shield would drop in place.

The apparatus may be utilized in searching for lost radioactive material by turning the sensi- A tivity control to its most sensitive-position, and carrying the instrument about the place where the presence of radioactive material is suspected. The indication on the meter will increase as one approaches the material, thus giving an indicative of its proximity. The apparatus may also be utilized for the relative measurement of quantity of radioactive material. For this purpose, a standardknown sample of material can be placed at .a definite position relativeto the apparatus. The reading is taken, after which the unknown sample is substituted in exactly the same spot and the reading is taken again. The reading will be in the ratio of the quantities. It. is to be noted that the apparatus. is linear, that the reading on the meter is exactly proportional to the frequency of pulses produced by the Geiger-Muller tube 24.

Where the hard gamma rays from radioactive material or the penetrating X-rays are of greatest interest, the case I may be made of steel and the case 22 surrounding the Geiger-Muller counter may be made of copper, approximately one millimeter thick. Where indications of less penetrating rays are desired, the case may be made of wood ,or plastic, and the surrounding tube 22 made of plastic. In the latter case, if shielding is found necessary due to the proximity of other circuit elements causing capacity disturbances, the tube .22 may be surrounded either with a grounded .pieceof screening or thin alu- *minum foil, either; of which will have .very little stoppi g power for the rays.

The apparatus :will necessarily respond to cosmicrays and the values of intensity as indicated will be thesum of that due to cosmic rays plusgam-marays and X-rays in the vicinity. If it is desired :to select an artificial zero as reference, one may, by adjusting the control 69,-set themeter to read zero in the presence of the ordinary cosmic rays plus whatever gamma rays are produced by, say the walls of the room in which the instrument is utilized. The instrument will then respond only :to increases above the usual gamma ray and :cosmic' ray background.

The .apparatusmay be. made operative by direct current at such voltages as six volts, 32 volts, 110 volts, and 220 volts, by usinga conventional vibrator type-inverter to convert the direct current to alternating-current. The-inverter unit may be fastened rigidly tothe under part of the case i and connections made to the inverter unit by plug. In this way, the: apparatus will become a universal type in which either direct current or alternating current may be'utilized.

Certain of the resistors and condensers have been designated as numbers '39, 6'5, and 84 to I00 inclusive. The functions of these have not been given in detail since their operation will be apparent from their relatiorrtothe remainder of the circuit elements.

Asuitablefset, of values and characteristics for a unit as shown,..isgiven below:

36-1 ampere fuse watt neon lamp ZB-Stancor P2751 transformer lt-ll'lZGGT 39-8 tmfd. 450 .volt

61-.01 mfd. 1-000 volt '8imfd. 600 volt it-0.1 meg. 54-6SF5 56-20 meg. 51-4 meg. 55-VR-l50 84-2000 ohm 8-5-50,000 ohm 49-2 meg. 50-.000075 mfd. 53-2 meg. 52-71 86-5,000 ohm 01-1-20 mfd. 88-.000075 mfd. 89-03 -meg. 9.0-.075 meg. 62-.00025 mfd. 93-2 meg. 94-5 meg. 63-10 mfd. 9I-20 meg. 92-1 meg. T8-.02,mf,d. EU-68R? fill-10,000 ohm 5-0 to v1 milliampere range 1l-0.2 meg. to.0.5 .meg. 96-2 meg.

10-T-2 neon lamp 13-.0005 mfd.

-.001 mfd.

91-50 meg.

99-25.,000 ohm [00-10 meg.

A suitable function to be served by theosclllatory circuit utilizing gas discharge lamp i0 is to change the range of the instrument instead of actuating analarm as shown.

One way in which this will be accomplished is as follows: The relay 16 instead of operating alarm elements could operate a switch placing an additional condenser in parallel with condenser 63. This would automatically change the range of the instrument. If desired, a signal such as a lamp 8 could be made to light by the same relay in conventional fashion, so that there will be an indication that a higher range isbeing utilized. Several ranges may be provided in this fashion by having several oscillatory circuits, each ceasing to function at a definite voltage, and each separately operating a relay placing still another condenser in parallel with condenser 63. The one system shown, can serve this function if the relay is a stepping relay such as that manufactured .by the American Automatic Electric Company,

each step providing an additional condenser in parallel with condenser 63. It is, of course, un-

derstood that the relay could in the same fashion The scope of the invention is indicated by the appended claims.

We claim:

1. A mounting for a Geiger-Muller tube comprising a rigid insulating base with a plurality of rigid conducting prongs, a conducting enclosure having ray transmitting properties for the rays to be measured by the Geiger-Muller tube completely enclosing the Geiger-Muller counter tube, the terminals of the said counter tube being connected respectively to the prongs, the external conducting enclosure being connected to an additional prong and supported by said base, thereby providing a convenient and easily connectible mounting for the tube.

2. A compact portable apparatus for measuring radioactive material, comprising an enclosing metallic case, a metallic frame within the said case, circuit elements disposed upon the said frame, the said elements including means to provide an operating voltage for a Geiger- Miiller tube and additional means to receive responses therefrom, a Geiger-Muller counter tube mounted vertically and supported by the said frame, the said frame, elements and Geiger- Miiller countertube being all enclosed within the said metallic case, the said Geiger-Muller tube further being provided with a removable enclosure so as to be removable from the said frame, the aforesaid combination of elements providing a unitary portable structure, with all parts rela' tively rigidly mounted.

3. A mounting for a member sensitive to radioactivity, said member having terminals for connection thereto, comprising an insulating base with a plurality of contacts, a conducting enclosure for the member sensitive to radioactivity, the terminals of the member sensitive to radioactivity and the conducting enclosure being connected to the contacts on the base, the enclosure being supported by said base and having ray 10 tube comprising a rigid-base having a longitudinal axis with a plurality of rigid conducting prongs insulated from one another, a Geiger- Miiller counter tube having'a longitudinal axis carried on said base, the terminals of said counter tube being connected to conducting prongs on the base the tube being mounted upon the base so that its axis is substantially parallel to that of the base thereby providing a convenient and easily connectable mounting for the tube. l

5. In an apparatus for measuring radioactivity, a frame assemblage having means mounted thereon for furnishing high voltage for a Geiger-Muller tube and for receiving the responses from the said tube, a Geiger-Muller tube having elements adapted to be maintained at high voltage relative to one another, the Geiger- Miiller tube being mounted upon a relatively rigid base member and in fixed mechanical re lationship thereto, relatively rigid prongs projecting from said base member connected to the elements of the said Geiger-Muller tube, the said base member and the prongs thereon engaging with a cooperating member relatively rigidly mounted upon the said assemblage so as to be electrically connected thereto and in proper rayreceiving relationship relative to the assemblage and the source of rays desired to be measured.

6. In a Geiger-Muller tube assemblage, a Geiger-Muller tube having a central conductor and an outer conductor, at least the said central conductor being of elongated form, a conducting shield placed exteriorly of the said Geiger- Muller tube, the said shield being of relatively elongated form positioned substantially co-extensive with the said central conductor, the said conducting shield being relatively transparent to rays from radioactive substances so that the said rays may pass therethrough and impinge upon the said Geiger-Muller tube, a relatively rigid base member aflixed to the said Geiger- Miiller tube and shield so as to maintain the two in proper relation to one another, the said base having relatively rigid conducting prongs projecting therefrom, the said prongs being connected to the said Geiger-Muller tube, the outer conducting shield being further connected electrically to a prong, whereby the said assemblage may be located and electrically associated with other apparatus. 7,

7. An apparatus as in claim 6 in which the said shield is made of sufficient thickness to effect substantial exclusion of beta rays, while at the same time being relatively transparent to gamma rays.

8. An apparatus as in claim 6 in which the shielding material is excluded from one side of the said shield, thereb making the assemblage especially sensitive to rays arising in the direction of the excluded portion of the said shield.

9. In an assemblage for detecting radiation, a relatively rigid base member having relatively rigid conducting prongs projecting therefrom, a Geiger-Muller tube attached to the said base and electrically connected to prongs contained therein, a conducting shield placed exteriorly of the said Geiger-Muller tube extending from and rigidly attached to the said base, whereby rays entering the said tube will first pass through the said shield, admitting rays it is desired to measure and aiding in the exclusion of other rays.

10. An apparatus as in claim 9, in which the 1 1 rigid base has a recessed portion formed therein and the shield fastened Within the'reces'sed portion.

11. An apparatus as in claim 9, in which the terminals of the Geiger-Muller tube are maintained at a high voltage relative to each other andthe external shield is maintained at ground potential. V

12'; A mounting for a Geiger-Muller counter tube comprising a rigid basewith a plurality of rigid conducting prongs insulated from one another, a Geiger-Muller counter tube carried on said base, the terminals of said counter tube being connected to conducting prongs on the base, an external conducting shield surrounding the said counter'tube through which shield all rays originating external to the said shield must pass before reaching the Geiger-Muller counter tube, the said shield being made of a selected thickness, and a selected material to provide the desired filtering characteristics for the rays passing therethrough to the counter'tube, and being additionally connected to one of the said conducting prongs to facilitate the electrical connection to the said conducting shield.

13. An apparatuses in claim 2, in which the case, frame and housing are all electrically in- 1 2 te'rccnne'ct'e'd and maintained ata definite reference potential.

MEYER JOSEPH TEST. SHELLEY- KRASNGW.

REFERENCES CITED The followingrefe'rences are of record in? the file of this patent? UNITED S IA'ISES PATENTS OTHER- REFERENCES Shrum and Smith;: CanadianJournal of Research, Vol.11, 1934, pp. 652'and- 655.

Kaiser: Review of Scientific Instruments, vol. 10, July 1939, DD. 218-219.

Curtiss: Journal-of Research of the National Bureau of Standards, vol. 23, July 1939, pp. 137- 143'.-

Lifschutz: Review of Scientific Instruments, vol. 10, January 1939; pp. 21-26. 

